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Wang Series 700B Advanced Programming Calculator Refurb.

BlaBla1985

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I tried to play back some of the tapes that have data on them (according to the labels stuff should be on there with verification codes and all)... but none of the 3 tape decks I have at hand work. Since I never use them i guess all the belts are gone. They don't transport the tape at all, or try to make tape salad (glad I caught that one on time).

That will have to be put off for now then, as I'll need some time to go over the other decks to see what would be needed to get those fixed. Maybe the 3rd belt I ordered fit any of the now not working decks to get one going again.

Please let us know if the belts end up working ok and what the ebay listing is. As Ill pick up a set for my 700.
I don't think the belts are a problem anymore, as the tape transports are very smooth now. Unless the motor is bad and the tape deck is no long running at the correct speed.

I used This one for the motor to the main flywheel

and This one from the flywheel to the tape transports
 
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durgadas311

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Another note on the tape heads. Unlike "hobby computers" that followed, Wang did not use audio signals for recording on tape. They used the same (mostly) "saturation" technique used by mainframes. This may demand a different kind of tape head. Note that Wang did not recommend the use of audio cassettes, although they seemed to work OK - but the higher quality, the better. "Chrome" or "metal" tapes would probably be best.

Note that a non-standard transport speed, as long as it is consistent for record and playback, should not be a problem for reading tape that was written on the same machine.

My point about trying to playback the tape on an audio deck was to test whether your machine is recording data on the tape. That would give us some idea as to whether the record circuitry is working. On load/read/playback, the Wang will hunt for clock signals in order to start loading. If it can't find a clock, it will just keep spinning tape. However, if the clocks end after some valid data, that data should have been loaded into memory.
Also note that the Wang depends on an End Prog code (EP) in memory, or on tape, in order to gracefully terminate the tape operation. I'm not sure what happens if there is no EP on a tape being loaded - it might just keep spinning tape, although it should have loaded bytes into memory. If it detects a parity error, it should stop immediate and go to the error state.

The tape load/store operations (microcode) are not terribly sophisticated, so probably don't tolerate hardware failures well.
 

BlaBla1985

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Quick look and all belts inside my double tape deck mini system have turned to goo, absolute mess. and it needs at least 2 belts per deck to work, so that won't be working in the short term. Need to order a bunch of belts to see what fits.

My point about trying to playback the tape on an audio deck was to test whether your machine is recording data on the tape. That would give us some idea as to whether the record circuitry is working. On load/read/playback, the Wang will hunt for clock signals in order to start loading. If it can't find a clock, it will just keep spinning tape. However, if the clocks end after some valid data, that data should have been loaded into memory.
Also note that the Wang depends on an End Prog code (EP) in memory, or on tape, in order to gracefully terminate the tape operation. I'm not sure what happens if there is no EP on a tape being loaded - it might just keep spinning tape, although it should have loaded bytes into memory. If it detects a parity error, it should stop immediate and go to the error state.
The audio playback test made sense to me, I just don't have working playback device now. It's all easily fixed with a few belts and some cleaning.
And if the data is recorded in a digital sense instead of as audio I can see how tape speed shouldn't matter too much as long as you use the tapes in the same tape deck. Could this mean that the tapes that were written back in the day might struggle to load because of the new belts?
I got a whole bunch of original Wang branded tapes with the machine, most with all sorts of stuff the original owner programmed on it, so the tape type should be good (although the magnetic tape might have failed). And one should be empty (nothing written on the labels).

From what I understand from the user manual I got with the machine, if you don't use an end program statement the machine will just keep loading until it runs out of Program Counter steps and then error out with one of the error lights above the keyboard.
Now, I know while recording the machine encounters the "program end" statement as it does stop automaticly while recording (the question I can't answer yet is if something got recorded on tape). But while loading it will just go on until it starts slipping on the clutch at the end of the tape.

Come to think of it... I have had the machine load a tape that (according to the labels) should have multiple programs on it. And after it went through the entire tape it hadn't errored out. I wonder if it's an allignment thing... might have to check that when i have time to open it up again. I say this because I have had it stop automaticly once or twice, but I'm not sure if any data was loaded from tape. And I think both times it was on the old belts.
 

BlaBla1985

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First link wont sell to the states, too bad. Second link appears to be incorrect.

hmm, turns out I derped with the second one, fixed it. But it's the same seller.

I should put the dimensions of the belts that came out of the tape deck and the ones I put into it into that workdocument. And update it to version 3 and upload it here.

I just picked the first seller I could find that had both belts in stock. From what i could see, all these belts come from China.
 

durgadas311

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I've seen scope kits that included some sort of "flux probe" (don't substitute a flux capacitor or paradoxes may result). You could probably make one from an old cassette tape drive head, or even an old radio part (ferrite core with a coil, with kapton tape to avoid any electrical contact). That way you could test whether the record head is delivering the desired signal. Testing the read head is a little more difficult, but you might be able to use a magnet to see if you can get a signal, or else a sine wave driving a coil. You'd need to look at the tape interface schematics to see where you watch the signals.

The idea being to test the circuits before you go to the trouble and risk of substituting a new tape head.
 

BlaBla1985

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I understand, to be honest I would rather not change out anything if it's not broken. I'll have to dig around the parts bins, I should have a tapehead somewhere. Although it might take a while to get going, work has been ramping up.

I will try to fix a regular tapedeck and do the experiment you suggested with recording something to see if the record head is working, having a working tape deck might be usefull anyway. Just need to guess the sizes of the belts needed.
 

BlaBla1985

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I've seen scope kits that included some sort of "flux probe" (don't substitute a flux capacitor or paradoxes may result). You could probably make one from an old cassette tape drive head, or even an old radio part (ferrite core with a coil, with kapton tape to avoid any electrical contact). That way you could test whether the record head is delivering the desired signal. Testing the read head is a little more difficult, but you might be able to use a magnet to see if you can get a signal, or else a sine wave driving a coil. You'd need to look at the tape interface schematics to see where you watch the signals.

The idea being to test the circuits before you go to the trouble and risk of substituting a new tape head.
When I was thinking about that fluxprobe made with a tape drive head, whould one of those cassette adaptors work?
cassette1.jpg
It's basicly what looks like a tape head, with a few resistors on a pcb.

cassette2.jpg

cassette3.jpg

And I know it works to play stuff, as it's still used to get audio from an Adlib card into the mini hifi I need to get belts for. This ofcourse works regardless of the belts condition. I wonder if it can also be used to pick up signals from the tape head in a tape drive...
 

durgadas311

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That sounds like a good plan, for testing the "playback" function at least. I'm not sure whether you can receive a signal back through that to test the Wang record function. If I recall correctly, there are separate record and playback heads... but I can't remember which schematic I need to look at to confirm. That's a stereo head, but I think that shouldn't matter.
 

BlaBla1985

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That sounds like a good plan, for testing the "playback" function at least. I'm not sure whether you can receive a signal back through that to test the Wang record function. If I recall correctly, there are separate record and playback heads... but I can't remember which schematic I need to look at to confirm. That's a stereo head, but I think that shouldn't matter.
Well, my intention was to hook up an oscilloscope to the 3,5mm jack and try to see if any signal would come out of the Wang. Mine indeed has only one head for both reading and recording (at least, I assumed it does both). And unless there is some form of diode inside the head in the cassette adaptor, I can't see a reason it would not pick up the signal from the Wang's tape deck.

Are there files (audio or other) available to inject a program into the machine via such an adaptor? It's not something i have looked for to be honest.
 

durgadas311

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That adapter has some interesting prospects, but of course depends on the Wang tape unit being functional. I have not tried to buy cassette tapes, so it could be like what's happening with floppy diskettes these - people are forced to find non-magnetic alternatives. It seems like one could devise something to digitize the signal and save it.

My one concern about that adapter is that it was designed to send signals to the tape player, not the other directions (automobile tape decks didn't usually have a record option). So, I think you could use it to inject a signal to the Wang and monitor that to see if the Wang receives it (i.e. test the Wang tape head), but I'm not sure what would happen if you used it to receive the Wang record signal. For one, that Wang does not use audio signals so I don't know how that adapter will react. In the same way, I doubt you could get that adapter to generate the signals expected by the Wang, such that you could get actual data loaded into the Wang. Again, electrically I think you can use it to test the Wang tape head. But I'm not sure it would work as a replacement for magnetic tape in "production" use.
 

mark0x01

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Dual heads are mainly found in premium cassette decks, so one is more common.
A second head was normally for erase, and can use either an ac or dc signal when active.
A drive heads for data would mainly be a mono head rather than stereo.

I would expect the adaptor's head to handle write as well as read, so worth experimenting, but the levels directly at the head will be quite low so may need amplification.

One thing to look for is head wear, which causes a noticable ridge at the edge of the tape path.
Degaussing can also improve signal, but that tool is uncommon now days.
A CRT degaussing wand could work at a pinch.
 

durgadas311

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Interesting tangent, the Wang 1200 Word Processing machine used dual-head *mono* - the tape heads read/wrote both "sides" at once. So, cassette tapes on that machine had only one side (could not be flipped over). They used one channel (side) for clock and the other for data.

Back to the 700, I think that cassette tape adapter would make a good test "probe" for checking out the tape unit, at least for confirming that the head is working. I suspect an oscilloscope attached to the adapter plug would show you some sort of activity when the Wang is storing a program to tape, which will tell if the data circuitry and tape head are functional. If you can get at the Wang signals (on P4) with an oscilloscope, you should be able to confirm that the tape head is receiving a signal (by playing audio through the adapter).

If you're not getting anything when the Wang is storing a program, it doesn't necessarily point to the tape head, as the record circuitry could also be bad. That's where injecting an audio signal into the adapter can tell you if the Wang head is working. If the head has been "blown", I won't work for record or playback. But if the head can receive a signal from the adapter, then it should also be able to generate a record signal (since it's the same head) so the fault would lie in the data circuitry.
 

BlaBla1985

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I would expect the adaptor's head to handle write as well as read, so worth experimenting, but the levels directly at the head will be quite low so may need amplification.
Thanks for the input, I should be able to find some time this weekend to set everything up and do some experimenting.

Back to the 700, I think that cassette tape adapter would make a good test "probe" for checking out the tape unit, at least for confirming that the head is working. I suspect an oscilloscope attached to the adapter plug would show you some sort of activity when the Wang is storing a program to tape, which will tell if the data circuitry and tape head are functional. If you can get at the Wang signals (on P4) with an oscilloscope, you should be able to confirm that the tape head is receiving a signal (by playing audio through the adapter).
Ah, that's a good point on using audio and measuring at the plug.

I was also thinking to go through the schematics and find the card(s) that send/receive data and look for any bad solder joints on the card(s) and use my thermal camera to see if any transistors or components get unusually warm/hot. I had a bad solder joint before on one of the dispay cards.
 

BlaBla1985

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I looked at the schematic for the card the tape deck connects to and inspected the card, nothing out of the ordinairy visually there. Then looked at the drives schematics and noticed that the tapehead is drawn as just a coil on 2 pins, not really sure what I was expecting to be honest... but I always thought a tapehead was more then just a coil (although in hindsight, it does make sense, as I believe most read/write heads are coils too).

The logical thing would've been ages ago to just measure the resistance of the head while unplugged from the machine. It reads open, which I guess means that there isn't a coil left in the head. I tried to measure it both on the head itself and on the connector to the rest of the machine, both open. The wirering from the connector to the head are good. So... my best guess now is that the head is just dead. No fancy experiments with scopes needed i suppose...

EDIT:

Connected the head to one of those cheap Ebay multi component testers and that claimed there is a 255pF cap in there. Using a multi meter results in a simular reading, a cap of around 284pF.
 
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durgadas311

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If the head was blown, the concern would be why and what will happen if you connect a good head in there (might keep blowing new heads). Perhaps there's a way to check out whether too much current is being passed through the head, by inserting some resistor in it's place. But, not sure what value to use. That would require doing something to measure the electrical signal at the "head", too.
 

BlaBla1985

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The resistor that is in line with the WDT signal in the schematic of the tape drive has drifted quite a bit... it measures 6.4kOhms, instead of 5.6kOhms (the colour coding is correct for a 5.6k resistor).

I'll see about turning the machine one tomorrow and do some testing anyway. I wonder if i can connect the scope across the head and see if signals come through. That could at least show that the machine side has some function to it.
I could still do the original idea anyway to see if anything gets through.

Looking at the schematic of the card that has the tape circuit on it, it seems pretty simple. One side takes a signal from the machine through a set of transistors and out to the WDT (which goes through the write protect switch onto the head), I'd guess that is the write signal.

Write.jpg

The other connects the 2 other signals from the heads through an amplifier and back into the machine. So I would guess that is the read side.

Read.jpg

And when I say it seems simple... I don't mean it is simple.
 

durgadas311

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Regarding 5.6K vs 6.4K, I think those resistors are 20% tolerance (no fourth color band). In which case, 6.4K is within the 20%. The difference may not indicate any aging of the resistor, it could have been the original value.
 

mark0x01

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Mono tape heads are still available new.
The tricky part might be matching the mounting, as there are many variations.
The resistance will be guesswork - usually around 100-300 ohms for cassette types, and you may need to modify the recording current 5k6 resistor for best results.
 
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